Category Example Source Effects and Associated Diseases

Mycotoxins Ergot alkaloids Claviceps fungi Gangrene, convulsions, abortion

Aflatoxins Aspergillus flavus Liver cancer

Tricothecenes Fusarium, Trichoderma Diarrhea, ataxia

Phytotoxins Cycasin Cycad flour Amyotrophic lateral sclerosis

Monocrotaline Senecio plants Hepatitis

Safrole Black pepper; oil of Sassafras Cancer

Solanine Solanaceae plants (potato) Neurotoxin

Animal toxins Venoms Snakes Cardiotoxin, neurotoxin

Bees Direct toxicity, cardiotoxin

Saxitoxin Dinoflagellates Neurotoxin, paralysis

Ciguatoxin Dinoflagellates Paresthesia, paresis, vomiting, diarrhea

Tetrodotoxin Puffer fish Neurotoxin, shock

Data from Hodgson E: Introduction to toxicology. In Hodgson E, Levi PE (eds): A Textbook of Modern Toxicology. Stamford, CT, Appleton & Lange, 1997, p. 1.

NATURAL TOXINS

In addition to manufactured pesticides, potent toxins and carcinogens are present in the natural environment, as summarized in Table 9-15 . These mycotoxins and phytotoxins may

contaminate foods. For example, cycad flour is used in arid climates. This plant contains the toxin cycasin (methylazoxymethanol b-glucoside). If the plant and seeds are cut into small

pieces, soaked in water, and dried, the toxin is leached. However, if these precautions are not followed, a degenerative neurologic disorder (amyotrophic lateral sclerosis) is produced by

ingestion of cycasin. Animal toxins can be ingested by eating fish, snails, or mollusks. The most common poisoning results from eating tropical fish and snails that have ingested

dinoflagellates containing ciguatoxin. Ciguatera

poisoning can be severe and occurs in the South Pacific and the Caribbean. Paralytic shellfish poisoning occurs in North America after eating mollusks that have ingested dinoflagellates

that contain saxitoxin. Aflatoxin B1 is produced by fungi that contaminate peanuts, corn, and cottonseed. It is a potent carcinogen that contributes to the high incidence of liver cancer in

some regions of Africa and the Far East ( Chapter 7 and Chapter 18 ).

RADIATION INJURY

Radiation is energy distributed across the electromagnetic spectrum as waves (long wavelengths, low frequency) or particles (short wavelengths, high frequency). The types, frequencies,

and biologic effects of electromagnetic radiation are summarized in Table 9-16 . Approximately 80% of radiation is derived from natural sources, including cosmic radiation, ultraviolet

light, and natural radioisotopes, especially radon gas. The remaining 20% is derived from manufactured sources that include instruments used in medicine and dentistry, consumer products

that emit radio waves or microwaves, and nuclear power plants. The potentially catastrophic effects of radiation are most vividly illustrated by the effects of nuclear explosions. The atomic

bombs dropped on Hiroshima and Nagasaki in 1945 not only caused acute injury and death but also increased incidence of various cancers among the survivors. Numerous historical

incidents document the deleterious effects of therapeutic radiation. For example, early in the 20th century, American radiologists experienced an increased incidence of aplastic anemia and

neoplasms of the skin, brain, and hematopoietic system. Children who were treated with radiation for an enlarged thymus or benign skin lesions between 1910 and 1959 suffered from an

increased incidence of thyroid abnormalities, thyroid tumors, and leukemias and lymphomas. Exposure of the fetus to radiation can produce mental retardation, congenital anomalies,

leukemia, and solid tumors. Investigation of these deliberate or accidental exposures to radiation led to an understanding of the relationship between the dose and timing of radiation and

the acute and chronic health effects. However, in general, these historical exposures were higher than radiation currently received by the general population from natural and manufactured

sources,

TABLE 9-16-- Ionizing and Nonionizing Electromagnetic Radiation

Date: 2016-04-22; view: 833